The present invention is directed to a ring interferometer comprising a single-mode light waveguide (optical fiber) which is wound into a form of a coil. Ring interferometers of this type are based on Sagnac effect. When the wound coil of the single-mode light waveguide is rotated relative to a reference system, and light is introduced into each end of a single-mode waveguide, a non-reciprocal transit time difference will be produced in the coil and can be interferometrically established. A typical application of a ring interferometer of this type is in the field of navigation.
It has been observed that the birefringent or double refractive properties of a typical single-mode fiber, which is being used caused by minor perturbations along the fiber, can lead to difficulties. In order to eliminate these difficulties it has been proposed that polarization filters whose direction of polarization are parallel to one another, are employed between the ends of each of the single-mode fiber and any detecting devices such as photodetectors. These solutions were discussed in two copending U.S. patent applications, Ser. No. 002,615, which was filed on Jan. 11, 1979, issued as U.S. Pat. No. 4,259,016 and corresponds to German application No. P 28 04 103, and Ser. No. 021,692, which filed Mar. 19, 1979 issued as U.S. Pat. No. 4,302,107 and corresponds to German patent application No. P 28 14 476. In addition, in copending U.S. patent application Ser. No. 002,537 issued as U.S. Pat. No. 4,325,636, which was filed on Jan. 11, 1979, and is based on German application 28 04 119, an interferometer of the above mentioned type, which utilizes directional couplers, was disclosed.